Tetrahydrofuran has been widely used in various fields as a solvent for various organic compounds or high polymers and also as an intermediate of various organic compounds. Recently, tetrahydrofuran has further found its use as a starting material or an auxiliary for synthetic polymers such as textiles and plastics, and thus is gaining increasing importance.
As one of processes for preparing tetrahydrofuran, there may be mentioned a process in which 1,4-butanediol (tetramethyleneglycol) is subjected to dehydration reaction in the presence of an acidic catalyst such as sulfuric acid and a cation exchange resin. (See, for example, Japanese Patent Publication No. 40699/1981 and Japanese Unexamined Patent Publication No. 108029/1982 and 108030/1982.)
The resulting reaction product obtained from the above dehydration reaction is a mixture of the desired tetrahydrofuran and water.
Therefore, in order to obtain tetrahydrofuran, it is necessary to isolate tetrahydrofuran from the reaction product. However, tetrahydrofuran and water constitute an azeotropic mixture and thus they cannot be separated from each other by a simple procedure.
From the viewpoint described above, there have been proposed the following methods for separating both components, tetrahydrofuran and water, from each other:
(1) a method in which distillation is effected in the presence of a drying agent such as sodium hydroxide and potassium carbonate; (2) a method in which an azeotropic distillation is effected in the presence of a third substance capable of constituting an azeotropic composition with at least one of both components; (3) a method in which an extractive distillation is effected in the presence of a solvent having an extremely strong affinity to either of both components.
However, in the above methods, a third substance having no direct relationship to the reaction system is employed and thus its procedure becomes complicated and cannot be an advantageous one for an industrial application.
Further, Japanese Patent Publication No. 39427/1978 discloses a method in which water contained in tetrahydrofuran is stripped by an azeotropic distillation under suitable conditions. However, it cannot be an advantageous one in which preparation steps are simplified.